The effect of an electrically large stirrer in a mode-stirred chamber

In a mode-stirred chamber, the field in the cavity is perturbed with a stirrer or rotating scatterer so that the time-averaged field is constant. The authors investigate the key factor that governs the effectiveness of a stirrer. By examining the fundamental properties associated with a perturbing body in a cavity, they find that the key to effective field perturbation lies in shifting the eigenmode frequencies. They illustrate this phenomenon by examining a two-dimensional cavity with a one-dimensional perturbing body. Using the transmission-line-matrix method, they compute the shifting of eigenfrequencies and examine the variation on the magnitude of the fields for different stirrer sizes. From this analysis, they draw an analogy between the action of a large stirrer and the effect of amplitude and frequency modulations. It is concluded that it is theoretically possible to simulate the stirrer by the external modulation of the input signal.>